In case of a reduction of focus-adjusting ability in the sense of sight, there have conventionally been used glasses 10 as depicted in FIG. 11 having a lens 11 for ordinary life and a lens 12 for seeing something nearby e.g., when reading a book or sewing, integrated into a single lens such that one of the two lenses is used depending on the angle of the line of sight of eyes so that an object can clearly be seen.
In other words, the user moves his/her eyeballs for use while being conscious of the upper side and the lower side so that an object of several meters or more in size or a scene is seen through the lens having its optical axis on the upper side and so that an object of the order of several tens of centimeters is seen through the lens having its optical axis on the lower side.
The user, however, needs to use the glasses while being conscious of, at all times, which lens of the upper and lower ones is being used. Further, in a case where careful attention is needed to peripheral objects while seeing an object at the center when doing a work nearby using the lower lens, the user has to follow the objects while turning his/her head since the angle of field is narrow. This results in a drawback that the user gets tired soon.
As a method for overcoming the drawback there has hitherto been proposed a variable-focus lens capable of adjusting its focal length depending on the distance to a target object. Proposed are ones (see, e.g., Patent Documents 1 and 2) having two transparent soft-elastic bodies with a transparent liquid or a gel-like substance confined therebetween so that the focal length is varied by changing the volume of the liquid or the gel-like substance; and one (see, e.g., Patent Document 3) having a transparent gel-like substance formed as a solid lens at one side and confined by a transparent soft-elastic film at the other side so that the focal length is varied by a deformation of the soft-elastic film.
It may be difficult, however, for the configuration of Patent Document 1 or 2 to obtain lens characteristics (accurate lens characteristics) as designed since the transparent soft-elastic bodies function as a lens under pressure. Further, in case of using as glasses, due to two faces made of the soft-elastic bodies, they may possibly often be deformed or damaged when touched by a finger or when hit by a flying fragment. It is thus necessary to cover at least one face in contact with the external world with a protective hood made of glass or plastic. Though Patent Document 3 solves the latter problem, difficulties still remain in control of the lens shape of the soft-elastic body and in acquisition of desired lens characteristics.